1. Field of the Invention
The present invention relates to an oil passage usable for an engine and more particularly to an oil passage usable for an engine, particularly, a four cycle internal combustion engine by way of which oil used in the interior of the cylinder head is smoothly returned to the crankcase.
2. Description of the Prior Art
As is hitherto known, oil supplied into the interior of the cylinder head is generally returned to the crankcase via a cam chain chamber formed in the cylinder block, stud bolt insert holes and the hollow space of the cylinder block after it lubricates operative parts in the valve actuating mechanism or the like arranged in the cylinder head or it cools them.
However, it has been pointed out as a drawback inherent to the conventional engine that oil is stirred by means of endless cam chain during returning to the crankcase via the cam chain chamber which constitutes a part of oil passage, resulting in air being entrapped in oil. Further, it has been found that as oil is scattered by means of the cam chain, a part of thus scattered oil is deposited on the valve actuating mechanism, causing an occurrence of mechanical loss relative to the latter, and another part of scattered oil is carried away together with blow-by gas, resulting in increased consumption of oil.
On the other hand, in the case where oil passage is constituted by a plurality of stud bolt insert holes there occurs a problem that a volume of oil to be returned is restricted because the diameter of insert holes can not be enlarged due to the geometrical configuration of the cylinder head and this leads to smooth returning of used oil to the crankcase being achieved only with much difficulties.